This invention relates to a fuel supply control method for internal combustion engines, and more particularly to such method which is adapted to increase the quantity of fuel being supplied to the engine to a quantity appropriate to the operating condition of the engine during acceleration of the engine while the engine is in a cold condition, thereby improving the accelerability of the engine.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Pat. No. 3,483,851, which is adapted to determine the valve opening period of a fuel quantity metering or adjusting means for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
Even though the above fuel supply control system is applied to an internal combustion engine, the fuel injected into the intake pipe of the engine is not vaporized to a sufficient extent when the engine is in a cold state, so that the mixture being supplied to the engine often cannot have a required air/fuel ratio, resulting in degradation in the driveability and emission characteristics of the engine. The rate of vaporization of fuel injected into the intake pipe is a function of the temperature of the engine as well as the pressure within the intake pipe. That is, the lower the intake pipe absolute pressure, the higher the rate of vaporization becomes. A fuel supply control method, which is based upon this fact, is known e.g. from Japanese Patent Publication No. 54-268, in which the fuel supply quantity is corrected by means of a correction coefficient which is a function of the engine temperature and the intake pipe pressure during normal operation of the engine while the engine is in a cold condition before it is supplied to the engine.
On the other hand, during acceleration of the engine, in order to enhance the accelerability of the engine, an increased quantity of fuel is supplied to the engine. The accelerating increment of fuel quantity should be set to a larger value when the engine is accelerated in a cold state, so as to compensate for a drop in the rate of vaporization of fuel as stated above.